Vinyl acetate monomer—a pilot plant study

The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid.     

Investigations of surface characterization of silicone rubber due to tracking phenomena under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric differential thermal analysis (TG-DTA) studies. The tracking time was different for a.c. and d.c. voltages.     

Modeling of optical low coherence reflectometry recorded Braggreflectograms: evidence to a decisive role of Bragg spectral selectivity

This paper draws attention to the basic principles governing reflections in uniform Bragg reflectors (BR) when measured employing optical low coherence reflectometry (OLCR) technique. Using computations based on transfer matrix method (TMM), we first showed a strong spectral dependence of Bragg reflectograms on an OLCR probe spectrum. Later, this dependence is exploited to evaluate, for the first time, the coupling coefficient κ of a Bragg grating in a distributed Bragg reflector (DBR) laser on InP     

Thoria doped with cations of group VB–synthesis and sintering

The cations M⁵⁺ (M=V, Nb and Ta) were doped in thoria through gel-combustion synthesis using citric acid as fuel. Thorium dioxide feed powders thus prepared were cold compacted without binder or lubricant and sintered to a high density (9.5 Mg m⁻³) at relatively low temperatures (1623 K). The powders were characterised for the residual carbon, crystallite size, specific surface area, particle size distribution and bulk density. The distribution of the dopant in the thoria matrix was analyzed by electron probe microanalysis. The reactivity of the calcined powders was determined by measuring the density of the sintered compacts prepared from them. For the first time it is demonstrated that apart from niobia, even tantala and vanadia can bring about accelerated sintering in thoria if they are doped through a wet chemical route viz., the gel-combustion procedure. The maximum densities obtained by doping with vanadia (0.02 mol%), niobia (0.50 mol%) and tantala (0.50 mol%) were 9.8 Mg m⁻³ (1573 K), 9.68 Mg m⁻³ (1423 K) and 9.69 Mg m⁻³ (1623 K), respectively.     

Ion implantation doping of OMCVD grown GaN

Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have indicated a redistribution in the measured profiles of Mg due to annealing.     

61单元分立式压电变形反射镜的研制

用于校正波前误差的61单元分立式压电变形反射镜是61单元自适应光学系统（AO）的关键器件之一。由于系统对单元数（61单元）和变形量（±3μm）的要求超过以往曾研制的变形镜，对研制工作带来许多困难。我们从理论分析到工艺研究采取措施，使研制的变形镜成功用于AO系统实验。     

Ductile-phase toughening and Fatigue-Crack Growth in Nb-Reinforced Molybdenum Disilicide Intermetallic Composites

A study has been made of the role of ductile-phase toughening on the ambient temperature fracture toughness and fatigue-crack propagation behavior of a molybdenum disilicide intermetallicmatrix composite reinforced with 20 vol pct niobium spheres. Using disk-shaped compact DC(T) samples, only moderate improvements (∼24 pct) in fracture toughnessK _lcvalues were found for the composite compared to the unreinforced MoSi₂ matrix material. Moreover, (cyclic) fatigue- crack propagation was seen at stress intensities as low as 75 to 90 pct ofK _Ic, with growth rates displaying a high dependency (∼14) on the applied stress-intensity range. The lack of significant toughening due to the incorporation of ductile Nb particles is associated with an absence of crack/particle interactions. This is attributed to the formation of a weak reaction-layer interface and elastic mismatch stresses at the crack tip between the Nb and MoSi₂, both factors which favor interfacial debonding; moreover, the spherical morphology of Nb phase stabilizes cracking around the particle. Results suggest that increasing the aspect ratio of the distributed Nb rein- forcement phase with attendant interfacial debonding and eliminating possible Nb-phase em- brittlement due to interstitial impurity contamination are critical factors for the successful development of tougher Nb/MoSi₂ structural composites. Formerly with McDonnell Formerly with McDonnell     

聚氧化乙烯—聚磷酸钠共混物的钠离子导电性

研究了聚氧化乙烯-聚磷酸钠共混物的钠离子导电性和低分子量多缩乙二醇对共混物导电性的改进作用。结果表明,降低多缩乙二醇的分子量以及增加其含量都有利于提高共混物的离子导电率。增塑剂改进共混物导电性的实质是提高共混物的非晶相含量,共混物内钠离子传导发生在非晶区,聚合物链段运动是离子传导的主要推动力。